How does the guest—host hydrogen bonding affect the thermal properties of clathrate hydrates?

Abstract

Herein, molecular dynamics simulations are performed to study the effect of the guest—host hydrogen bonding on the thermal properties, such as isothermal compressibility, isobaric thermal expansivity, and heat capacity, in the sI clathrate hydrate phases of trimethylene oxide (TMO), ethylene oxide (EO), and formaldehyde (FA) as polar guests. The results of these simulations are compared with those of nonpolar guests with analogous structures, cyclobutane (CB), cyclopropane (CP), and ethane (Et). Binary hydrates are constructed with the above guests in large 14-sided cages and methane placed in small 12-sided cages of the structure of sI clathrate hydrates. We present the temperature dependence of the lattice parameter and also the pressure dependence of the unit cell volume for variety guests with different sizes, polarity, and guest—host hydrogen bonding capability. The lattice parameters for some of the guest species obtained in this work are in good agreement with experimental values. The oxygen atom of the formaldehyde carbonyl group and the ether oxygen atoms of TMO and EO molecules can form hydrogen bonds with sI large cage water hydrogen atoms while CB, CP and Et molecules do not. The consequences of the guest—host hydrogen bonding on the isothermal compressibility, thermal expansivity, and heat capacity of the clathrate are discussed.